Evaporator vacuum pump



Sept. 22, 1964 J. P. PAPAC OSTA ETAL EVAPORATOR VACUUM PUMP Filed Sept.29, 1959 fie. 3.

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United States Patent 3,149,716 EVAPORATOR VACUUM PUMP John P. Papacosta,Los Altos, and Robert W. Crews, Palo Alto, Calif., assignors to A. B.Dick Company Filed Sept. 29, 1959, Ser. No. 843,224 1 Claim. (Cl.206-.4)

This invention relates to an evaporative, inorganic vapor-type of vacuumpump, and, more particularly, to improvements therein.

Evaporative, inorganic, vapor-type non-magnetic vacuum pumps usuallyfind application in the vacuum-tube art. After a vacuum-tube envelopehas been pumped by the usual mechanical or diffusion pump to as low apressure as is obtainable therewith, the evaporative, inorganic vaporpump is employed. Effectively, this comprises a filament upon whichmetal has been crimped. The filament is then heated electrically,whereby the metal crimped thereto may adsorb, or absorb, or chemicallycombine with atoms or molecules of different gases, removing them fromthe volume to be evacuated. When the metal crimped on the filament isheated to sublimation or evaporation, its vapor is deposited as a filmon cooler surrounding surfaces, trapping the gas in and beneath thefilm.

In the metal crimped on the heating filament, oftentimes because of poorthermal contact with the filament, would not sublimate but would meltand form an amalgam with the filament. When an amalgam is formed, thefilament becomes brittle and easily breaks with further heating. Thus,the formation of an amalgam is not desired. Upon heating the filamentmany times, the crimped metal would fall from the filament because thefilament would become deformed as a result of being heated and the crimpwas not always effective to hold the metal to the filament. If thefilament is not thoroughly cleaned (a. difficult thing to do), thenbecause of the nonuniform contact between the filament and the crimpedmetal thereon, due to oil or other dirt on the surface of the filamentand/or metal, a good heat transfer does not occur between the filamentand the metal. Therefore, the metal is not heated to sublimation, but,rather, melts, and then amalgamates with the filament.

An object of this invention is to provide an improved evaporative vacuumpump of the type described wherein amalgamation between the metalattached to the filament and the filament is avoided.

Another object of the present invention is the provision of anarrangement for an evaporative vacuum pump of the type described,wherein a uniform contact is assured between the metal segments mountedon the filament, and the filament.

Yet another object of the present invention is the provision of a novel,useful, and more efficient evaporative type of pump than heretoforeobtainable.

These and other objects of the invention are achieved in an arrangementwherein metal segments, such as titanium or zirconium, are spotwelded toa stretched helical tungsten filament which is supported within theregion to be evacuated. Because of the use of the spotweld technique forattaching the metal segment to the filament, a uniform contact isassured. Thus, when the filament is heated, the segments effectively gofrom the metal to the gaseous form without melting, and therefore noamalgamation with the filament occurs. As a result, substantially allthe metal attached to the filament is used for pumping.

3,149,715. Patented Sept. 212 1964 The novel features that areconsidered characteristic of this invention are set forth withparticularity in the appended claim. The invention itself, both as toits organization and method of operation, as well as additional objectsand advantages thereof, will best be understood from the followingdescription when read in connection with the accompanying drawing, inwhich:

FIGURE 1 is a perspective drawing of a tube illustrating the location ofthe embodiment of the invention therein;

FIGURE 2 is a drawing of a section along the lines 22 of FIGURE 1,showing the embodiment of the invention; and

FIGURE 3 illustrates a detail of the invention.

In FIGURE 1 of the drawing there is shown how the embodiment of theinvention may be employed with a tube 10. Two feed-through pins 12, 14are used to connect heating power to the embodiment of the inventionwhich is an evaporative pump mounted inside the tube.

Referring now to FIGURE 2, which is a section taken along the lines 2-2of FIGURE 1, there will be seen an embodiment of the invention. Thiscomprises a stretched helical tungsten filament 16, which is supportedwithin a frame. This frame includes the pair of lead-through pins 12,14, which extend through the tube envelope 16. A nickel bar 18 is weldedto one of the lead-through pins 14. A support bar 20 is welded at rightangles to the nickel bar 18. The tungsten wire filament is attached toand stretched between the support bar 20 and the leadthrough pin 12. TheWeld joint of support bar 20 maintains it in position. In accordancewith this invention, metal segments 22 which may either be titanium orzirconium are tack-welded to the tungsten filament. The segments areheld against the tungsten filament with a light pressure during welding,and a current is applied sufficient to provide tack welding. FIGURE 3 isa detail showing a metal segment 22 tack welded to the filament 16.

A source of electrical heating energy 24 is connected through a switch26 to the lead-through pins 14, 12, whereupon the tungsten filament willheat up. It is heated sufficiently to sublimate the metal segments. Inview of the uniform and intimate contact assured by the tackweldingtechnique, rather than the crimping technique used heretofore, there isno amalgamation between the metal segments and the filament.

The operation of the metal, which is called trapping or gettering, maybe accomplished at different temperatures as the metal heats up. It maybe accomplished either by the metal segments themselves or in the vaporwhen the metal is heated to evaporation. The metal vapor is deposited asa. film on the cooler surrounding surfaces of the tube envelope, wherebythe gas is trapped in and beneath the film. The operation of the pumpmay be occasional, cyclical, or continuous to achieve the desired amountof evacuation. Such evacuation occurs in the pressure range between 10-and 10* millimeters of mercury. The pump may be operated in conjunctionwith other devices, such as ion gages or ion pumps, to effect suitablepumping characteristics.

The construction and operation of the pump is simple, convenient, andeconomical, and no magnetic fields are required to be employedtherewith. The envelope with which the pump is used may be of anysuitable metal, ceramic or glass. Accordingly, a novel and improvedevaporative vacuum pump has been described hereinabove.

References (Iited in the file of this patent UNITED STATES PATENTS BoerMay 17, 1932 Flory Feb. 6, 1940 De Boer et al. June 11, 1940 VandergriftApr. 1, 1941 Record Mar. 10, 1942 Agule May 31, 1960

